As a method for detecting a nucleic acid molecule having a particular target nucleic acid sequence, a hybridization method using a probe having a base sequence complementary to the target nucleic acid sequence is widely used. In the hybridization method, a probe having a base sequence complementary to the target nucleic acid sequence is prepared, and only a sample having a base sequence complementary to the base sequence of the probe hybridizes with the probe with high selectivity. As a method for detecting a hybrid formed as a result of hybridization, a method of labeling a probe nucleic acid with a radioisotope, a method of labeling with a fluorescent substance, a method utilizing a luminescence reagent and the like can be mentioned. A fluorescent substance that can be used for labeling a nucleic acid includes fluorescein, tetramethylrhodamine, Cy3, Cy5 and the like. However, fluorescent nucleic acid probes labeled with these fluorescent substances mainly utilize a FRET type mechanism based on a combination of a fluorescent agent and a quencher, and the extinction coefficient of fluorescence is merely about 98%. Therefore, the background fluorescence signal is high and high sensitivity measurement is difficult.
To solve the above-mentioned point, a fluorescent compound that becomes fluorescent due to a chemical reaction on a template has been developed. However, since such fluorescent on/off switchable compounds (patent documents 1 and 2) generate fluorescence by a reduction reaction of an azido group, there is a problem that a reducing agent phosphine is easily oxidized in a solution.